Kinetics and Mechanism of the Substitution Reaction of Amine in (bis(Acetyle Acetonato) Ethylenediimine(Diamine)Cobalt(III) Perchlorate with N3-, Br- and NCS-)

A series of complexes of the type trans-[Co(acacen)(amine)2]ClO4, where (acacen) is the (bis(acetyleacetone) ethylenediimine) and the amines are Benzyl amine (bzlan) 1, 2-amino pyrimidine (2ampy) 2, N-methylpipirazine (nmpip) 3, 3-methyl pyridine (3mpy) 4, p-toluidine (p-toldn) 5, has been synthesized and characterized by uv-vis. and FT-IR. The kinetics of the substitution reaction of [Co(acacen)(p-toldn)2]ClO4 with N3- , Br- and NCS- ions has been investigated in an aqueous solution by using UV-vis. spectroscopy. It has been found that the reaction occurs in two steps, hydrolysis and ligation. The first order rate constants for hydrolysis and ligation reactions in 313K have been determined. The rate of reaction is almost independent of the type and the concentration of anion. So, the interchange dissociative (Id ) mechanism is suggested. The reaction has been carried out in several temperatures and the activation energy for hydrolysis and ligation (for NCS- anion) reactions have been calculated about 55 and 95 kJ/mol respectively.